Control.AllowDrop 屬性
定義
重要
部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。
取得或設定值，指出控制項是否能接受使用者拖放上來的資料。
public:
virtual property bool AllowDrop { bool get(); void set(bool value); };public virtual bool AllowDrop { get; set; }member this.AllowDrop : bool with get, setPublic Overridable Property AllowDrop As Boolean屬性值
如果控制項內允許拖放作業，則為 true，否則為 false。 預設為 false。
範例
下列程式碼範例可讓使用者將影像或影像檔拖曳到表單上，並將其顯示在卸載的點。 系統會 OnPaint 覆寫 方法，在每次繪製表單時重新繪製影像;否則，影像只會持續到下一次重新繪製為止。 DragEnter事件處理方法會決定要拖曳到表單中的資料類型，並提供適當的意見反應。 如果 Image 可以從資料建立 ，事件 DragDrop 處理方法會顯示表單上的影像。 DragEventArgs.X由於 和 DragEventArgs.Y 值是螢幕座標，所以此範例會使用 PointToClient 方法來將它們轉換成用戶端座標。
private:
Image^ picture;
Point pictureLocation;
public:
Form1()
{
// Enable drag-and-drop operations and
// add handlers for DragEnter and DragDrop.
this->AllowDrop = true;
this->DragDrop += gcnew DragEventHandler( this, &Form1::Form1_DragDrop );
this->DragEnter += gcnew DragEventHandler( this, &Form1::Form1_DragEnter );
}
protected:
virtual void OnPaint( PaintEventArgs^ e ) override
{
// If there is an image and it has a location,
// paint it when the Form is repainted.
Form::OnPaint( e );
if ( this->picture != nullptr && this->pictureLocation != Point::Empty )
{
e->Graphics->DrawImage( this->picture, this->pictureLocation );
}
}
private:
void Form1_DragDrop( Object^ /*sender*/, DragEventArgs^ e )
{
// Handle FileDrop data.
if ( e->Data->GetDataPresent( DataFormats::FileDrop ) )
{
// Assign the file names to a String* array, in
// case the user has selected multiple files.
array<String^>^files = (array<String^>^)e->Data->GetData( DataFormats::FileDrop );
try
{
// Assign the first image to the picture variable.
this->picture = Image::FromFile( files[ 0 ] );
// Set the picture location equal to the drop point.
this->pictureLocation = this->PointToClient( Point(e->X,e->Y) );
}
catch ( Exception^ ex )
{
MessageBox::Show( ex->Message );
return;
}
}
// Handle Bitmap data.
if ( e->Data->GetDataPresent( DataFormats::Bitmap ) )
{
try
{
// Create an Image and assign it to the picture variable.
this->picture = dynamic_cast<Image^>(e->Data->GetData( DataFormats::Bitmap ));
// Set the picture location equal to the drop point.
this->pictureLocation = this->PointToClient( Point(e->X,e->Y) );
}
catch ( Exception^ ex )
{
MessageBox::Show( ex->Message );
return;
}
}
// Force the form to be redrawn with the image.
this->Invalidate();
}
void Form1_DragEnter( Object^ /*sender*/, DragEventArgs^ e )
{
// If the data is a file or a bitmap, display the copy cursor.
if ( e->Data->GetDataPresent( DataFormats::Bitmap ) || e->Data->GetDataPresent( DataFormats::FileDrop ) )
{
e->Effect = DragDropEffects::Copy;
}
else
{
e->Effect = DragDropEffects::None;
}
}
private Image picture;
private Point pictureLocation;
public Form1()
{
// Enable drag-and-drop operations and
// add handlers for DragEnter and DragDrop.
this.AllowDrop = true;
this.DragDrop += new DragEventHandler(this.Form1_DragDrop);
this.DragEnter += new DragEventHandler(this.Form1_DragEnter);
}
protected override void OnPaint(PaintEventArgs e)
{
// If there is an image and it has a location,
// paint it when the Form is repainted.
base.OnPaint(e);
if(this.picture != null && this.pictureLocation != Point.Empty)
{
e.Graphics.DrawImage(this.picture, this.pictureLocation);
}
}
private void Form1_DragDrop(object sender, DragEventArgs e)
{
// Handle FileDrop data.
if(e.Data.GetDataPresent(DataFormats.FileDrop) )
{
// Assign the file names to a string array, in
// case the user has selected multiple files.
string[] files = (string[])e.Data.GetData(DataFormats.FileDrop);
try
{
// Assign the first image to the picture variable.
this.picture = Image.FromFile(files[0]);
// Set the picture location equal to the drop point.
this.pictureLocation = this.PointToClient(new Point(e.X, e.Y) );
}
catch(Exception ex)
{
MessageBox.Show(ex.Message);
return;
}
}
// Handle Bitmap data.
if(e.Data.GetDataPresent(DataFormats.Bitmap) )
{
try
{
// Create an Image and assign it to the picture variable.
this.picture = (Image)e.Data.GetData(DataFormats.Bitmap);
// Set the picture location equal to the drop point.
this.pictureLocation = this.PointToClient(new Point(e.X, e.Y) );
}
catch(Exception ex)
{
MessageBox.Show(ex.Message);
return;
}
}
// Force the form to be redrawn with the image.
this.Invalidate();
}
private void Form1_DragEnter(object sender, DragEventArgs e)
{
// If the data is a file or a bitmap, display the copy cursor.
if (e.Data.GetDataPresent(DataFormats.Bitmap) ||
e.Data.GetDataPresent(DataFormats.FileDrop) )
{
e.Effect = DragDropEffects.Copy;
}
else
{
e.Effect = DragDropEffects.None;
}
}
Private picture As Image
Private pictureLocation As Point
Public Sub New()
' Enable drag-and-drop operations.
Me.AllowDrop = True
End Sub
Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)
MyBase.OnPaint(e)
' If there is an image and it has a location,
' paint it when the Form is repainted.
If (Me.picture IsNot Nothing) And _
Not (Me.pictureLocation.Equals(Point.Empty)) Then
e.Graphics.DrawImage(Me.picture, Me.pictureLocation)
End If
End Sub
Private Sub Form1_DragDrop(ByVal sender As Object, _
ByVal e As DragEventArgs) Handles MyBase.DragDrop
' Handle FileDrop data.
If e.Data.GetDataPresent(DataFormats.FileDrop) Then
' Assign the file names to a string array, in
' case the user has selected multiple files.
Dim files As String() = CType(e.Data.GetData(DataFormats.FileDrop), String())
Try
' Assign the first image to the 'picture' variable.
Me.picture = Image.FromFile(files(0))
' Set the picture location equal to the drop point.
Me.pictureLocation = Me.PointToClient(New Point(e.X, e.Y))
Catch ex As Exception
MessageBox.Show(ex.Message)
Return
End Try
End If
' Handle Bitmap data.
If e.Data.GetDataPresent(DataFormats.Bitmap) Then
Try
' Create an Image and assign it to the picture variable.
Me.picture = CType(e.Data.GetData(DataFormats.Bitmap), Image)
' Set the picture location equal to the drop point.
Me.pictureLocation = Me.PointToClient(New Point(e.X, e.Y))
Catch ex As Exception
MessageBox.Show(ex.Message)
Return
End Try
End If
' Force the form to be redrawn with the image.
Me.Invalidate()
End Sub
Private Sub Form1_DragEnter(ByVal sender As Object, _
ByVal e As DragEventArgs) Handles MyBase.DragEnter
' If the data is a file or a bitmap, display the copy cursor.
If e.Data.GetDataPresent(DataFormats.Bitmap) _
Or e.Data.GetDataPresent(DataFormats.FileDrop) Then
e.Effect = DragDropEffects.Copy
Else
e.Effect = DragDropEffects.None
End If
End Sub
給繼承者的注意事項
在衍生類別中覆 AllowDrop 寫屬性時，請使用基類的 AllowDrop 屬性來擴充基底實作。 否則，您必須提供所有實作。 您不需要同時覆寫 get 屬性的 AllowDrop 和 set 存取子;您可以視需要只覆寫一個。
